An investigation into the effect of Gd on the optoelectronic properties of ZnO waveguide thin films by prism coupler

Abstract

GdxZn1−xO (x=0, 0.005, 0.01, 0.02, 0.04) films were elaborated via spray pyrolysis on ordinary glass to explore GdZnO's potential as a waveguide. X-ray diffraction showed the incorporation of Gd in the wurtzite structure with decreasing crystallite size and a pronounced alignment along the [002] direction. UV-Vis measurements indicated a 0.02 eV increase in the optical gap energy, starting from 3.24 eV. Hall effect measurements showed a 104 decrease in charge carriers' density, mobility increase up to 209 cm2/Vs, and a 103 increase in magnetoresistance. Photoluminescence spectra of the films revealed the presence of different kinds of point defects with a slight tendency to promote Zni and VO defects. Atomic force microscopy assessments depicted randomly oriented and elongated grains over Gd doping and overall smoother films. The waveguide properties of the films were investigated using the prism coupler techniques. A slight and general decrease was observed in ordinary refractive indices going from 1.9745 in the ZnO film to 1.9713 in the Gd0.02Zn0.98O film while the extraordinary refractive index decreased from 1.9777 to 1.9692. The birefringence was inverted for all the doped films except for Gd0.04Zn0.96O film as it experienced no guiding modes at all. The simulated results were highly aligned with the prism coupler model of distinct interfaces and step refractive index.